The present invention relates generally to a formulation for providing corrosion protection to metallic reinforcement members in concrete. More particularly, the present invention relates to a formulation and method for employing concrete sealers containing migrating corrosion inhibitors together with a component for enhancing the compatibility of the sealer component with the inhibitor component for the purpose of providing long-term protection to metallic reinforcement members contained within the body of the concrete structure.
In U.S. Pat. No. 5,597,514 (hereinafter the "'514 patent"), assigned to the same assignee of the present invention, a process is described in which corrosion inhibitors are added to the raw concrete mixture to provide for long term corrosion protection of the surfaces of the metallic reinforcement members. Pursuant to the processes of the '514 patent, corrosion inhibitors are added at an amount sufficient to provide long term protection to the metallic reinforcement for extended periods of time. This process is adapted very well for use with fresh or new concrete and presently is being widely used throughout the world.
In accordance with the present invention, formulations have been developed for use as surface treatments on existing concrete structures to form coatings and/or sealers which contain corrosion inhibitors. This seal coat protects the concrete while resisting penetration of harmful chemicals and at the same time slowly releases corrosion inhibition chemicals into the concrete, thus protecting the embedded metallic reinforcements. When used in combination with concrete which contained corrosion protection as described in U.S. Pat. No. 5,597,514, a more effective system is provided.
The present system of sealers or seal coating formulations containing corrosion inhibitors in accordance with the present invention is especially useful with older or exposed concrete structures in need of a means of retarding the ongoing metallic corrosion.
Parking ramps, bridges, driveways, and garage floors that typically require sealing and resealing are typical applications for the present system. Indeed, the formulations of the present invention have been found to be highly useful and perform exceptionally well when utilized on concrete surfaces which have undergone surface checking or the like, or alternatively have experienced some erosion or loss of surface. The formulation is effective because of enhanced compatibility of the components leading to equally enhanced performance.
It is common practice to utilize salts such as sodium chloride and/or calcium chloride as a component to lower the freezing point of ice and/or snow, and these materials have created persistent problems in structures such as parking ramps, bridges, and driveways. Because of the corrosive nature of these salts, damage to metallic reinforcements including rebar, mesh, screen, and the like has occurred. Deterioration of the concrete structure follows, and extensive repairs and occasionally rebuilding of the structures must be undertaken. Because the use of these chemicals is constantly increasing, and since the corrosion to the metallic reinforcements proceeds without interruption and on a constant basis, systems and/or techniques are required in order to either arrest and/or retard the chemical reactions which occur and lead to the deterioration of the reinforcements and ultimately to the concrete structures per se.
Reinforced concrete structures are typically provided with steel bars and/or rods (rebar) for longitudinal tension reinforcement as well as compression reinforcement, and reinforcement against diagonal tension. Expanded metal, steel-wire mesh, hoop iron or other thin rods may be embedded in the concrete structure for reinforcement purposes. Being ferrous-based materials, and as indicated hereinabove, the integrity of the reinforcement is subject to deterioration whenever exposure to chloride-containing salts, oxides of sulfur or nitrogen occurs. When mixtures containing the formulations of the present invention are utilized in sealing the concrete, significant protection of the reinforcement is obtained due to the passivating effect of the migrating corrosion inhibitor on the embedded metal, which leads to a significantly lower rate of deterioration.
Because the nature and properties of concrete structures limit and/or bar ready access to the interior of the structure, coating the exterior surface provides a mechanism for reducing the ingress of corrosive materials and thus reduce the rate of the reactions occurring along the surfaces of the metallic reinforcements. The exterior surfaces provide a host location and invasive point for the corrosive salts. Since these surfaces are normally exposed and available for coating, the preparation and utilization of desired sealers and/or seal coats containing corrosion inhibitors in accordance with the present invention may be undertaken. The seal coat formulations of the present invention have sealing properties matched to the task, and are tough and durable, and hence are capable of providing reasonably long term protection for concrete structures. The corrosion inhibiting components of these same formulations show enhanced compatibility with the sealer components with the result being improved performance of the overall combination.
The formulations of the present invention provide coatings, which when cured, provide a desirable balance of properties with respect to porosity, water absorption and water resistance. While most coating formulations compounded for the coating of concrete exhibit a certain amount of porosity, it has been found that a certain degree of porosity may be a desirable feature for the coating, particularly when applied directly onto the host surface. Thereafter, one or more additional coatings may be applied to the surface in order to assist in forming an appropriate seal. The use of a coating formulation which provides a modest amount of porosity has been found to provide more rapid and controllable leaching of the corrosion inhibiting component into the bulk of the concrete being protected. In other words, the film forming component of the coating applied directly to the surface of the concrete has a modest tendency to provide a porous surface in order to permit initial leaching or slow migration of the corrosion inhibiting chemical from the body of the film to the surface of the concrete. Thereafter, the leached corrosion inhibitor migrates from the surface to the internal portions of the concrete structure. By way of example, excessive porosity is undesirable, and may be controlled and/or avoided by multiple coatings or selection of formulation materials such as coatings having a high degree of toughness, ability to fill holes, and to otherwise protect the concrete surface. Formulations based substantially on sodium silicate have shown an ability to seal concrete through filling of pores and/or holes, and this affects migration of the migrating corrosion inhibitor substantially. Other coating bases such as silicone (siloxane) with higher solids and one trip coatings have been found to provide uniform and sound coatings. However, the ability to seal the surface and fill holes in the substrate does not perform as well as multiple coatings with sodium silicate base materials, and the corrosion inhibitor migrated at a significantly more rapid rate. For certain applications, however, such a coating may be helpful in providing a material for reaching the metallic reinforcements at an earlier point in time. The formulations of the present invention further include a compatibility enhancing component which enhances the performance of the overall sealant/inhibitor formulation by enhancing the compatibility of the individual components.